Magnetic positioning device

ABSTRACT

A TWO-AXIS MAGNETIC SYSTEM FOR DRIVING CHART PLOTTERS AND OTHER DEVICES. A MARKER CARRYING HEAD FLOATED ON AN AIR BEARING OVER A PLATEN WITH NO MECHANICAL INTERCONNECTIONS. A PLURALITY OF ELECTROMAGNETS IN THE HEAD AND MEANS FOR SELECTIVELY ENERGIZING THE ELECTROMAGNETS   TO MOVE THE HEAD ACROSS THE MAGNETIC PLATEN, AND ALONG BOTH AXES SIMULTANEOUSLY IF DESIRED.

July 18, Ql a. A. SAWYER MAGNETC POSITIONING DEVICE 2 Sheets-Sheet l`Original F'ilscl Hay 31, 1966 /Z y f 16716: 5.

n.. m #n ,w E@ H fu www, 1 M

n Ma www E3. A. SAWYER MAGNETC POSITIONING DEVICE July 18, i972 2Sheets-Shee ,2

Original Filed May 3l, 1956 mada by reissue.

States Matter enclosed in heavy brackets [1 appears in the originalpatent but forms no part of. this reissue specification; matter printedin italics indicates the additions ABSTRACT OF THE DISCLOSURE A two-axismagnetic system for driving chart plotters and other devices. A markercarrying head floated on an air bearing over a platen with no mechanicalinterconnections. A plurality of electromagnets in the head and meansfor selectively energizing the electromagnets to move the head acrossthe magnetic platen, and along both axes simultaneouly if desired.

This invention relates to plottcrs and toV drive systems suitable foruse with plotters and other positioning devices. The system of theinvention will be described initially as incorporated in a chart orgraph plotting device but other applications will be readily apparentand some will be described.

.In a typical system, a picce'of paper is placed on a platen or platemember and a moving element or head member carrying a chart marker ismoved over the paper. The chart marker may make a continuous line or anintermittent line or may be operated under the control of an externalsource making a mark as desired. A variety ot' chart markers ispresently available and may be ultilized with the system of thoinvention.

It is an object of the invention to provide a new and improved systemwhich is small, light and of low inertia. while having high resolution,accuracy and repeatability. A particular object is to provide such asystem which may be used with any of a wide variety of signal sources.An additional object is to provide a system which may be entirelydigital in operation. A further object is to provide a system which maybe analog, wholly or in part.

It is an object of the invention to provide a new and improved systemincorporating a magnetic drive for the movingr member and one requiringno mechanical connections to the moving member. An additional object istto provide such a system which does not require any position feedbackor followup information for its operation. Another object is to providesuch a system which may utilize a feedback control if desired.

lt is an object of the invention to provide a drive systern for use inplotters and the like, which system will provide the propulsionfor-producing the relative motion between the members, the control ofthe relative position ot the two members, and restraint against rotationof one member relative to the other, all acting aiong each of two axesand independently of each other in response to input information. Theinput information may be digital in neutre with the motion occurring indiscrete steps witch are repeatable and which may be made very small.

lt is i object of the invention to provide a system for Contre trotative movement of two members incorporating a r te member having1 atone surface thereof an altern-ating :fut-ern of nonmngnetic material andmagnetic material. 1. head member having first and second parallel setsof magnets aligned with the pattern, cach of the attent Re. 27,435Reissued July 18, 1972 magnets having a pole face at a surface of theheadmember positioned adjacent the plate member surface, with the setshaving corresponding magnets, and means for selectively energizingcorresponding magnets of the sets for producing relative movementbetween the members along the pattern.

It is an object of the invention to provide a system for independentstepwise relative movement of two members along two axes incorporatingva plate member 'having at one surface'thereof a grid of nonmagneticmaterial enclosing zones of magnetic material with the grid defining afirst axis and a second axis in the plane of the surface, a head memberhaving a first set of magnets aligned with the irst axis and a secondset of magnets aligned `with the second axis with each of the magnetshaving a pole face at a surface of the head member positioned adjacentthe plate member surface, means for selectively energizing magnets ofthe rst set for producing relative movement between the members alongthe first axis, and means for selectively energizing magnets of thesecond set for producing relative movement between the members along thesecond axis.

It is a further object of the invention to provide such a system whereinthe head member has a first tet of magnets aligned with the first axis,a second set o! magnets aligned with the second axis, a third set ofmagnets dlrposed parallel with the first ret, and a fourth ser ofmugncts disposed parallel with the second set, with the en ergizingmeans selectively energizing corresponding magnets of the tirst andthird sets and corresponding magnets of the second and fourth sets forproducing the relative movements.

It is an object of the invention to provide such a system including atool carrier for a chart marking pen or the like mounted on the headmember. A further object is to provide such a system incorporating meansfor spacing the head member from the plate member, typically a fluidbearing comprising means defining at 'least one cavity at the surface ofthe head member and means for directing a stream of fluid under pressureinto the cavity for outward flow between the surface to the surroundingatmosphere.-

It is an object of the invention to provide a system incorpomting newand improved magnetic structures for precise control of the relativemovement of the members and for providing very small and repeatableV.stepping increments. An -additional obiect is to provide such asystern wherein the sets of magnets may comprise various numbers ofindividual magnets as desired providing 'for various so-calledmultiphase operation, with the threemagnet set and three-phase drivingsystem being .presently preferred. A further object is to provide sucha. system which may incorporate full-step operation and partial-stepoperation by varying the sequence in which the magnets of a set areenergized and/orcthe magnitudes of the magnet energizing currents.

The invention contemplates the utilization'of a `plate member and a headmember, with the head member separate from and movable along a surfaceof the plate member and with first and second pluralities of controlledelectromagnetic elements in one of Said members and disposed along firstand second axis, respectively. The system further contemplates means forenergizing selected elements of the first plurality for producing forcesbetween the members holding the members against relative movement alongthe lirst axis and for changing the selected elements for producingforces between the memhersproducing relative movement along the firstaxis, and similar independent means for energizing selected elements olthe secondary plurality for controlling relative movement along thesecond axis.

Y The invention also comprises novel details 'of construcion and novelcombinations and arrangements of parts, which will more fully appear inthe course of the followng description. The drawings merely show and thedescription merely describes preferred embodiments of the presentinvention which are given by way of illustration or example.

In the drawings:

FIG. 'l is a perspective view of a preferred embodiment of the inventionillustrated as a chart plotter;

FIG. 2 is a bottom isometric view of the head member of the system ofFIG. 1;

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2'.

FIGS. 4 and 5 are enlarged partial sectional views taken along the lines4-4 and 5-5, respectively, of FIG. 2, showing the head member positionedover the plate member;

FIG. 6 is a diagram of an electrical driving circuit for energizing thehead member;

FIG. 7-'is a view similar to that of FIG. 2 showing an alternative formof the head member;

FIG. 8 is an enlarged isometric view of one of the magnets of FIG. 7;

FIG. 9 ,is a view similar to that of FIGS. 2 and7 showing anotheralternative form of the head member;

FIG. l is a partial sectional view taken along the line 10-10 of FIG. 9;and

FIG. l1 is a side view illustratingv another embodiment of theinvention.

The system as illustrated in FIGS. 1-6 includes a plate member 10 and ahead member 1l. The upper surface o! the plate member carries a grid 12of nonmagaetic material enclosing zones of magnetic material, with thegrid defining first and second axes which normally are orthogonal. Theseaxes are sometimes referred to as the X axis and the Y axis.

Typically the plate member 10 may be a sheet 14 of ferromagneticmaterial such as iron, having a plurality of parallel grooves 15 formedtherein, with one set of grooves normal to the X axis and another set ofgrooves normal to the Y axis. Zones or teeth of magnetic material 16project upward between the grooves. In the preferred structureillustrated in the drawings, the grooves are at right angles to eachother and are equally spaced along both axes, leaving the projectingzones of magnetic material of square cross section. In a typicalstructure, the grooves or slots 15 are .D30-inch wide and .D30-inch deepand are spaced .O30-inch apart along both axes. The grooves may be leftopen with the air serving as a nonmagneticA material, but it ispreferred to lill the grooves with a plastic or other nonmagnetic solidto provide a smooth upper surface for the plate member.

In a typical plotter, a sheet of paper 20 rests on the plate member 10and the head member moves over the sheet 20. If desired, means may beprovided for holding the paper in position bodiment is-illustrated inFIG. l. A manifold 21 is positioned on the underside of the plate member10 and communicates with a plurality of openings 22 provided in theplate member. The openings i riphery of the grid 12 and may beinterconnected by a channel 23 inthe upper surface of the plate memberif desited. Openings mayals6 be provided over the face of the grid ifdesired. A vacuum may be applied to the manifold 21 via line 2.4 forholding the paper down against the upper surface of the plate member 10After a marking operation is completed, a slight pressure may be appliedon the line 24 providing a lifting force on the sheet 20.

The head member includes four sets 27. 28, 29, of magnets mounted in abase 31 with the pole faces of the magnets at the surface of the base.In one form of cons :'uction, the base 31 may be a cast plastic memberwith z embedded therein with the magnet pole faces 32 im. r .wrm-f. nfthe base. such as is shown in FIG.

on the plate member and ofte em- 22 may be around the pe-v lll) faces isnot limited to that illustrated.

,s is the distance between the i face 32 has one or more ridges ofmagnetic 3. Each pole material and preferably is provided with appraliaJ spacing as the zones 16 m iigridges of the same width andmagnetic material in the plate member. The set o? nets 27 and the set ofmagnets 29 are disposed p one of the axes oi the grid, say the X axis,and are to propel and position the head member along the X a. Similarly,the sets 28 and 30 are utilized to propel :rnd position the head memberalong the other axis, typically the Y axis. The sets of magnets may beidentical in construction and set 27 is shown in FIG. 3 comprising anIrl-shaped core 33 (which could be an assembly ot lamination stampings)with a pole face 32 at the end of each arm and with a coil 34 disposedabout each arm. A plate 35 oli magnetic material may be afiixed to thetops of the cores 33, as shown in FIG. 3, to act as back iron for thereturn ux. The operation of the system is the same for motion along eachaxis and it may be operated to provide simultaneous motion along bothaxes to produce a diagonal motion or may be operated to provide motionalong one axis and then along the other. Operation along one axis withthe sets 21, 29 wm b described in conjunction with F1os. 4 and S,recognizing that operation along the other axis will be the same. i

. Magnetic coupling is utilized between the head member and the platemember for moving and positioning or restr ining the head member withrespect to the plate FIG. 4 illustrates the condition with the coil Vol?`the: B"r`nagnet of the set 27 energized and with the coils of the A andC magnets unencrgized, Under these conditions, the head member is movedto bring the ridges ot magnetic material in the pole face of the lt:magnet into alignment with the zones of magnetic material in the platemember. In the multiridge pole face illustrated, the spacing between thecenter lines ot the two adjacent vridges of the pole faces of the A andB magnets and the spacing between the center lines of the two adjacentridges of the pole faces of the B and C magnets is V3 of the pitch ofthe grid on the plate member, where the pitch is the distance from thecenter line of one groove or one tooth to the center line of the nextgroove or tooth.

.It the C magnet is energized and the B magnet is deenergized, the setof magnets will be moved to the right ils of the pitch to bring the poleface of the C magnet into alignmentwith the zones of magnetic materialoE the platen or plate member. If the C magnet is now deenergized andthe A magnet lis energized, the head member will be moved to the rightanother 1/3 oi the pitch. De-energizing the A magnet and energizing theB magnet will move the head member to the right another'/s pitchbringing it back to the condition illustrated in FIG. 4. Il the B magnetis now cle-energized and the A magnet is energized, the head member,will be moved to the left 1/5 pitch. Thus it is seen that the headmember may be moved relative to the plate member in a stepwise manner byenergizing the magnets of the set in the appropriate sequence. Thethree-magnet set illustrated requires three driving currents and issomtimes referred to as a threephase system. It should be noted that afour-phase or higher phase system could be utilized if desired.

It should be noted that the spacing between the pole The system willoperate with any spacing that satisfies the expression:

:Muti/rp) where:

or of adjacent or outer ridges of the pole faces of the mamets which areenergized in sequence irl-the stepping operation,

p is the pitch of the grid,

n is an integer, l. 2, 3, and j is the number of phases of the systemand i; greater than two.

center lines of the pole faces" Referring to FIG. 5, it should he notedthat in the "ict set 29, the spacing between the centerlines of adjacentridges of the pole lacesis /2 of the pitch il'lcsequence of the threemagnets of the set is the e oi the sequence 0F, the three magnets of theset 27. 5 liown in FIG. 4. The operation is the same as deied inconjunction with FlG. 4. Consider the situation rc the magnets B, B' areenergized initially. r[hen the r cnets B, B are cle-energized and themagnets A, A' ur: energized. This will cause both magnet sets to move tothe left providing aiding forces for moving the head iember. li thesequence of magnets is the same in both sets, the spacing between thepole faces should be the same, that is, both should be pin-Hhs) or bothshould be p(n-1/1). Where a reverse sequence is utilized in one set, thespacing of one set should be pn-l-l/e) and the spacing of the other setshould be p(nl/). In FIG. 4,

dn -=l, and in FIG. 5, n=2.

The use of two sets of magnets disposed in parallel produces a balancedpair of tangential forces which act on the head member in the horizontalplane, and hence tend to eliminate a net torque about an axis normal tothe plate when the head is stepping. The use of two sets also producesresisting torques tending to lock the head against rotation about theaxis normal to the plate when the head is static. The use of thereversesequence tends to eliminate torques acting on the head memberabout an axis parallel to the plate or pole faces. This is be cause thenormal components oi attractive force are caused to act at points nearlyeqnidistant and on opposite sides of the centroid of the head member.

A typical electrical driving circuit for one axis is shown in FIG. 6 andincludes a'three-stage ring counter 40 and amplifiers 41, 42, 43 whichprovide the current for energizing magnets AA', BB', and CC',respectively. The amplifier 41 will be energized when the counter 40 isin the A stage, the amplifier 42 will be energized when the counter isin the B stage, and the amplifier 43 will be energized when the counteris in the C stage. A pulse on the +X input to the counter will advancethe counter in the positive direction, i.e., from A stage to B stage orB stage to C stage or C stage to A stage. Similarly, a pulse on,the Xinput will advance the counter in the opposite direction.

Any suitable source may be utilized to provide the pulses to the counterinput for driving the head member relative to the plate member. 'Ihesystem illustrated is completely digital in operation, with the headmember advancing one step in the positive direction for each pulse onthe plus input line and one step in the negative direction foreach"pulse on the minus input line. In the embodiment being described,one step is equivalent to 1/3 pitch. In an alternative arrangement, aso-called half- Step operation can he achieved, in which each step `is1/6 pitch. In this mode of operation, the magnets of a. set areenergized in the sequence A, AB, B, BC, C, CA, A, etc., producingmovements per step one half that achieved with the sequence A, B, C.This half-step mode of operation is readily achieved by modifying thelogic circuits of the ring counter.

Oth'er alternative arrangements may be utilized in higher phase systems.For example, in a five-phase system with magnets, A, B, C, D -and E, thesequence A, 1B, C. D, E, A or the sequence A, AB, B, BC may be used. Thepreferred sequence for magnet energization in n tive-phase system is AB,ABC, BC, BCD, CD, CDE, DE., DEA, EA, EAB, AB. This sequence providessubstantinlly equal tangential forces for each step and also provides areduction in normal force variations. Similar results may be achievedwith the 2. 3, 2, 3, sequence in higher odd phase systems, such as sevenand nine.

Means ire usually provided for spacing the head memler from the platemember to prevent direct contact belV-rcn the members or between thehead member and the paper resting on the plate member andtherebyeliminate friction forces between the two members. Variousarrangements may be used, including fluid bearings, wheels or balls. lnthe embodiment of FIGS. l-6, a cover 46 or housing is positioned overthe magnets and engages the base 31 in sealing relation. A control line47 is terminated at the cover 46 by a coupling 48. The control `line 47includes a conduit for a supply of liuid under pressure into the housing46 and a cable for the electrical connections to the magnets. Thecontrol line 47 preferably is a highly tiexible line which providessubstantially no loading on the head member. A plurality of openings 49through the base 31 provides for air ilow from the interior of the headunit to the bottom surface thereof. Grooves 50 may be provided in thebottom surface of the base 31 linking the openings 49. Typically airwill be used as theuid, but other gases and liquids may be utilized fordifferent applications.

` With this arrangement, there is a constant tiow of air through thecontrol line 47 into the housing 46, through the openings 49 and outwardto the atmosphere between the bottom surface of the head member and thetop sur face of the plate member. This air flow provides an air bearingbetween the two members. The attraction force provided by the magneticcoupling between the members and the repulsion force provided by the airbearing are balanced by appropriate adjustment of the air bearingorifice characteristics and the air supply pressure to main tain thehead member at a substantially constant spacing above the plate member,typically ln the order of one to a few thousandths of an inch.

The air bearing spacing system may take various forms and onealternative embodiment is illustrated in FIG. 7. A cavity 53 a fewthousandths of an inch deep is provided in the bottom face of the base31 centrally positioned between the pole faces of the magnet. The airconduit in the control line 47 is branched into four separate lineswhich terminate at four openings 54 positioned in the cavity S3. Withthis construction, there is no pressure differential across the housingof the head member and problems of leakage are substantially eliminated.

Referring again to FIG. l, an appropriate tool carrier 57 is mounted onthe head member 11 and typically may be disposed at one corner of thehead member. The tool carrier is adapted for carrying a `tool forengaging the plate member or a sheet of material positioned on the platemember. A wide variety of devices is avalbale for this use and typicallymay comprise a marking pen with a solenoid for moving the pin into andout of engagelment with the chart paper. The electrical control for sucha marking pen may be contained in the control line 41.

An alternate form of magnet construction is also illustrated in the headof FIG. 7 and one magnet thereof is shown in greater detail in FIG. 8.Coils7 58, 59 are positioned on the arms of a Ulshaped armature 60, withthe coils connected in series or in parallel to provide aiding flux inthe core. Pole faces 61, 62 are carried at therespective ends of theUshaped core 60 (which could be made of lamination stampings), the polefaces preferably being grooved in the same manner as the pole face 32 ofFIG. 3, with the two pole faces spaced the widthiof one groove so thattwo pole faces 61, 62 provide a plurality of uniformly spaoed groovesand lands or ridges. Another alternative construction for the headmember 1s illustrated in FIGS. 9 and l0 with the housing removed. Themagnet construction may be in the form4 shown in FIGS. l-dor in FIGS. 7and 8, but with the coils and cores carried on a top member 65 and thepole faces carried in the base 31 with a small air gap between the coresand pole faces. The cores may have a wider-section 33a at the air gap.The top member 65 is supported from the base 31 by a exure supportstructure which may comprise a plurality of flexible rods 66, typicallyfour rods disposed at the corners of the head member. The air bearingspacing system of FIG. 7 may be utilized with two outlets` 54 in thecavity 53. The housing normally is carriwtl on the top member 65. Thetool carrier may be supported from the top member 65 or from the oase3i, de

if lling upon the type of operation desired.

basic purpose of the construction of FIG. 9 is to the stepping speed.Each time the head is caused to ep very large accelerations areproduced. At very high steppimy rates the peak forces required to act ontit: head would be very large. l, however, the mass that is acted upondirectly is made small, such as the thin base plate 31, then the peakforces will be reduced by the ratio ot' the masses. Since it is notessential that the much larger mass of coils and cores be accelerated atthe high rates of the base, the former can be coupled to the latterthrough flexible elastic elements. These are made flexible in thetangential direction and stiff in the support direction. Damping meansmay be used to prevent uncontrolled oscillations of the top relative tothe base` Another alternative embodiment is illustrated diagrammaticallyin FIG. 11 and includes the head member 11 disposed above the platemember 10. A support sheet 67 is positioned above the head member 11,and a follower unit 68 rests on the support sheet. Typically the supportsheet 67 may le a thin sheet of plastic or other nonmagnetic materialwhile the follower unit 68 and the head member 11 have coactingpermanent magnets therein tor coupling the follower unit to the headmember. The iullower unit may incorporato a fluid bearing supplied in nline 69. Another tlultt bcnrlng muy bo utilized between the plate (i7und the hond member l1 it desired. With this embodiment, the toolcarrier may be mounted in the tollower unit or at the corner thereof andthe chart paper or other material to be marked may rest on the supportplate 67. The structure of FIG. l1 is especially suited for a highperformance plotter, some advantages of which are: (l) very small, lightfollower unit which could be easily removed and replaced; (2) excellentchart visibil ity, including the option of back lighting through thesupport plate 67 (if translucent); (3) easy conversion to transformplotter into automatic or semi-automatic curve follower by replacingmarker of unit 68 with optical pickup head; (4) high speed, highperformance head member 11. The efciency of producing tangential forcesby the pole face to plate relationship is greatly increased. Since thereis no paper in the air gap between the head member 11 and the platemember 1l), the total gap can be made of the order of l mil, or about1/s the total gap if paper is interposed.

While the system of the invention has been described above asincorporating two sets of magnets -disposed in parallel for each axis ofmotion, the system may be utilized with only one axis and two spacedparallel sets of magnets. In another alternative arrangement, the systemmay be operated for two axes with only one set of magnets per axis.

While the invention has been described aboye in thc form of ahorizontally disposed chart marking device, it is readily useful forother purposes and in other orientations. The system may be utilized togenerate relative motion between the head member and the plate memberfor any functions which can be programmed. The plate member may bedisposed vertically to provide for writing or drawing in a verticalplane. The entire system may be inverted with the head member restrainedto provide motion of the plate member over the head member. With thisarrangement, the plate member could carry a workpiece and the systemcould be utilized to digitally drive the workpiece past an operatingstation,

ine.

sazc'u as a machine tool cutting edge. The tool carrier,

of course, may be utilized to carry a wide variety of tools in additionto a chart marking pen and one typical application is an engraving toolwhich may be utilized in conjunction with nonrnagnetic metals and otherumleiiuls.

Although exemplary embodiments ot the invention liste been disclosed anddiscussed, it will be understood 8 that other applications of theinvention are possible and that the embodiments disclosed may besubjected to various changes, modifications and substitutions withoutnecessariiy departing from the spirit of the invention.

I claim as my invention:

1. In a system for controlling relative movement of two members alongtwo axes, the combination of:

a plate member;

a head member separate from and movable along a surface of said platemember;

a first plurality of controlled electromagnetic elements in only one ofsaid members disposed along a rst axis;

a'second pluarlity of controlled electromagnetic elements in said onemember disposed along a second axis, with the other of said membershaving a layer of material providing a continuous magnetic path;

means for energizing selected elements of said rstv plurality forproducing forces between said members holding said members againstrelative movement along saidv lirst axis and for changing the selectedeleinents for producing forces between said members producing relativemovement along said first axis; and

means for energizing selected elements of said second yplurality torproducing forces between said mem 'i bei; holding said members againstrelative move t vtraint along tutti cond nxt und for changing theselected elements to: producing forces between .salti membm producingrelative movement along salti second axis.

2. In a system for relative moveemnt of two mem bers along twoaxesnhecombination of:

a plate member having at one surface thereof a grid of nonmagneticmaterial enclosing zones of magnetic material, said grid defining afirst axis and a second axis in the plane of said surface;

a head member having a rst set of magnets aligned with said rst axis, asecond set of magnets aligned with said second axis, a third set ofmagnets disposed parallel with said rst set, and a fourth set of magnetsdisposed parallel with said second set,

cach of said magnets having a pole face at a surface of said head memberpositioned adjacent said piate member surface, said first and third setshaving corresponding magnets and said second and fourth sets havingcorresponding magnets;

means for selectively energizing corresponding magnets of said first andthird sets for producing relative movement between said members alongsaid rst axis; and

means for selectively energizing corresponding magnets of said secondand fourth sets for producing relative movement between said membersalong said second axis.

3. A system as defined in claim 2 including a tool carrier mounted onsaid head member and having. means for carrying a tool directed towardsaid surface of said plate member. l

4. A system as defined in claim 2 including means for spacing said headmember from said plate member.

5. A system as defined in claim 4 wherein said spacing means comprisesmeans defining at least one cavity at said surface of said head memberand means for directing a stream of iluid under pressure into saidcavity for outward flow between said surfaces.l

6. A system as defined in claim 2 wherein the sequence of the magnets ofsaid rst set is the reverse of the sequenct of the corresponding magnetsof said .third se?. and the sequence of the magnets of said second setis the reverse of the sequence of the correspondiig magnets of thefourth set.

7. A system as def-med in calim 2 wherein the sequence ot the magnets ofsaid first set is the reverse follower member and means for supportingsaid head follower member in parallel relation with said head member,said head member and head follower member including interacting magneticcoupling means for coupling said members together so that the headfollower member duplicates the movement of the head member.

means tot' cnetgtzing magneti provides tot energizing the magnets of ttniet itt the sequence A, AB, D, 11C),

of the the sequence of the corresponding magnets of said third set andthe sequence of the magnets of said second set is the reverse of thesequence of the corresponding magnets of the fourth set, and the spacingof one of said first and third sets and of one of said second and fourthsets, between the ccnterlines ot' pole faces of magnets in theenergizing sequence, is p(n-|-l/rp) and the span ing of the other ofsaid first and third sets and of the other of said second and fourthsets is pfn-l/p) where n is any whole number, p is the pitch of the gridand qa is the number of phases of the system.

8. A system as defined in claim 2 wherein said head 9. A system asdefined in claim 2 including a head Y 10. A system as defined in claim 2in which said I means for energizing magnets provides for energizing themagnets ot a set one at a time.

il. A system as, defined in claim 2 in which laid where A, and Cdesignata individual magnets. i2. In a system for relative movement oftwo members,

the combination of:

for spacing said head member from said plate member comprising meansdefining at least one cavity at said surface of said head member andmeans for directing a stream of fluid under pressure into said cavityfor outward flow between said surfaces.

14. In a system for stepwise relative movement of two members along twoaxis, the combination of:

a plate member having at one surface thereof a grid of nonmagneticmaterial enclosing zones of mag-l netic material, said Igrid defining afirst axis and a second axis in the plane of said surface;

a head member having a first set of magnets aligned with said first axisand a'second set of magnets aligned with said second axis, each of saidmagnets having a pole face at a surface of said head member positionedadjacent saidmlate member surface;

means for selectively energizing magnets of said first set for producingrelative movement between said members along said first axis; and

means for selectively 'energizing magnets of said second set forproducing relative movement between said members along said second axis.

in'. In a plotter for making charts and the like, the

combination of:

t: plate member having at one surface thereof a grid of nonmagneticmaterial enclosing zones of magnetic material, said grid dcning a firstaxis and a second axis in the plane of said surface;

a head member having a first set of magnets aligned with said firstaxis, a second set of magnets aligned with said secondaxs, a third setof 'magnets disposed parallel With said first set, and a fourth set ofmagnets disposed parallel with said second set,

cach of said magnets having a pole face at a surface of said head memberpositioned adjacent said plate member surface, said first and third setshaving corresponding magnets and said second and fourth sets havingcorresponding magnets,

said head member including means defining at least one cavity at saidsurface of said head member;

means for directing a stream of fluid under pressure into said cavityfor outward fiow between said surfaces;

a chart marker carried on said head member positioned for marking on achart resting on said one surface of said plate member;

means for selectively energizing corresponding magnets of said first andthird sets for producing stepwise relative movement between said membersalong saidxrst axis; and

means for selectively energizing corresponding magnets of said secondand fourth sets for producing step- Awise relative movement between saidmembers along saidsccond axis.

16. Afplotter as defined in claim 15 wherein said cavity iii centrallydisposed in said surface of said head merinber with' said pale facespositioned around said cav ty.

17. A plotter tts defined in claim t6 wherein nach 'of said tats ofmagnets comprises three magasin, with the sequence at the magnets oftite third set being the reverse of the sequence of the magnets of thetrst set and with the sequence of the magnets of the fourth set beingthereverse of the sequence of the magnets of the second set.

18. A plotter as defined in claim 15wherein said zones of magneticmaterial are substantially equally spaced along said axis and whereineach of said pole faces extends over a plurality of said zones, witheach pole face having a plurality of rows of magnetic material spaced bynonmagnetic material, with the spacing of said rows substantially thesame as -the spacing of said zones.

19. A system as defined in claim 2 in which said means for energizingprovides for energizing the magnets of a set in the sequence AB, ABC,BC, BCD, CD, CDE,

DE .,'twhere A, B, C, D and E. designate individual magnets.

20. In a plotter for making charts and the like, the

combination of:

a first plate member having at one surface thereof a grid of nonmagneticmaterial enclosing zones of magnetic material, said rgrid defining afirst axis and a second axis in theplane of said surface;

a second plate member disposed in spaced relation with said first platemember;

a head member having a first set of magnets aligned with said firstaxis, a second set of magnets aligned with said second axis, a third setof magnets disposed parallel with saidfirst set, and a fourth set ofmagnets disposed parallel with said second set,

each of said magnets having a pole face at a vfirst surface Vof saidhead member positioned adjacent said first plate member surface, saidiirst and third sets having corresponding magnets and said second andfourth sets having corresponding magnets,

with said head member disposed between said plate members and includingmeans defining at least one cavity at said rst surface and at a surfaceopposite said first surface;

a head follower member including means defining at least one cavity at asurface thereof' and disposed adiacent said second plate member;

13 ing at least one element for interacting magnetically with the gridstructure of the first member to provide a rlisphuetnent of the firstmember relative to the seco/ul member along the second axis, theelements ln the third means being displaced relative to cach other andto the grid structure of the first member to provide for thedisplacement of the second tnernber relative to the first member alongthe second axis.

27. In the system set forth in claim 26:

the first and second members being planar and being disposed incontiguous relationship to each other.

28. In the system set forth in claim 26:

the first member having magnetic characteristics the second meansincluding first windings selectively energized for obtaining a magneticinteraction of the ,rst means with the rst member to produce a force fordisplacements between the first and second members along the first axiswhen selectively energized and the third means including second windingsselectively energized for obtaining a magnetic interaction of the secondmeans with the first member to produce a force for displacements betweenthe first and second members along the second axis when selectivelyenergized.

29. ln a system for providing a controlled relative movement between twomembers along rtt and second t-nnllnnte ares, the combination of:

n first member,

n second member spaced from the first member tutti movable relative tothe ,first member along first and second coordinate axes and includingfirst magnetic means for interacting magnetically with the first memberto drive the second member relative to the first member only along thefirst axis and including second magnetic means for interactingmagnetically 1..'th the first member to drive the secondv member,independently of but simultaneously with the operation of the firstmeans, relative to the first member only along the second axis andinhibiting rotation of the second member relative to the first memberabout an axis substantially normal to a surface defined by the first andsecond axes,

third means for providing for a selective energizing of the first meansto obtain a selective driving of the second member relative to the firstmember along the first axis, and

fourth means for providing for a selective energizing of the secondmeans to obtain a selective driving of the second member relative to thefirst member along the second axis.

30. In the system set forth in claim 29:

the first member being in the form of a grid and the rst and secondmembers being constructed to provide simultaneous but independentmovements of the second member relative to the first member alo'ngl thefirst and second coordinate axes.

31. In the system set forth in claim 29:

the first and second members being planar and being disposed incontiguous relationship to each other.

32. In the system set forth in claim 29.'

the first magnetic means being magnetically interactive with tite firstmember for providing for the determination of the position of the secondmember relative to the first memben alo'ng the first axis while drivingthe second member relative to the first member along the first axis andthe second magnetic means being magnetically interactive with the firstmember for providing for the determination of the position of the secondmember relative to the first member along the second axis while drivingthe second member relative to the first member along the seco/nl axis.

33. In the sys-:enz set forth in claim 30:

the first member being in the form of a magnetic grid lll) 14 a'nd therst and second magnetic means in the second member being constructedwith magnetic properties for cooperation with the magnetic grid toprovide displacements along the first and second coordinate axes antithe third and fourth means rtfspectlvely including first and secondwindings rt!n spectlvely coupled magnetically to the first and seca andmagnetic means. 34. In the system set forth in claim 29: the first andsecond members having magnetic prop erties and the first magnetic meansand the second magnetic means being operative magnetically upon thesecond member to aect the magnetic properties of the second member and,in accordance with the magnetic interaction between the first and secondmembers, the magnetic properties of the first member to obtain a drivingof the second member relative to obtainy a driving of the second memberrelative to the first member along the first and second axes. 35. In asystem for providing a controlled relative movement between two membersalong first and seco'nd coordinate axes, the combination of:

a rst member,

a second member spaced from the first member and movable relative to thefirst member along the rst and second coordinate ares dnd includingfirst magnella means for producing a magnetic interaction with the firstmember to `drive the second member rela! c to the rst member along thefirst asis amt for s multansetttly providing for a tietennlmtrtnn nf theposition of thstvccntt member relative m the first member along thefirst esta and fun/ter including second magnetic means for producing amagnetic interaction with the first member to drive the second memberrelative to the first member along the sec ond axis simultaneously withthe drive of the second member relative to the first member along thefirst axis and for simultaneously providing for a determination of theposition of the second member rela tive to the first member alo'ng thesecond axis,

third means for providing for a selective energizing of the firstmagnetic means to obtain a selective driving of the second memberrelative to the first member along the first axis, and

fourth means for providing for a selective energizing of thesecondvmagnetic means torobtain a selective driving of the second memberrelative to the first member along the second axis.

36. In the systemset forth in claim 35:

the first and seco'nd members being constructed to provide simultaneousbut independent movements of the first member relative to the secondmember along the first and second coordinate axes.

37. In the system set forth in claim 35:

the first member being in the form of a magnetic grid and the first andsecond means being provided with magnetic properties and being disposedfor magnetic cooperation with the first member to provide arbitrarymovements along the first and seco'nd axes and the third 'and fourthmeans respectively including rst and second windings respectivelycoupled magnetically tofthe first and seco'nd magnetic means.

38. In the system set forth in claim 35:

the firstand second members being planar and being disposed incontiguous relationship to each other.

39. In a system for providing a controlled relative movement between twomembers along firstand second coordinate areas, the combination of:

a first member,

a second member disposed relative -to tlze first 'member andselectively' energizable for producing a magneticforce between the firstand second members to provia'e an independent movement of the secondmember relative to the first member along the first axis,

second magnetic means disposed on the second member and selectivelyenergl'zable for producing a magnetic force between the first and secondmembers to provide an independent movement of the second member relativeto the first member alqng the second axis simultaneously with themovement'iof the second member relative to the first member along thefirst axis,

third means for selectively energizing the first magnetic means, and

fourth means for selectively energizing the second magnetic means.

tbl In the system set forth in claim 39.'

the first and second members being constructed relative to each other toprovide discrete movements of the first member relative to the secondmember along the first and second axes. v

4l. In the system set forth in claim 39:

the first and second members having magnetic characteristics anti thet/iird means including first windings energizabie to produce a magneticforce between the first member and the first magnetic means forproviding a movement of the second member relative to the first memberalong the first axis and the fourth means including second windingsenergizable to produce a magnetic force between the first member and thesecond magnetic means for providing a movement of the second memberrelative to the first member along the second axis.

42. In the system set forth in claim 39:

the first means being constructed to inhibit rotation of the second member relative to the first member about an axis substantially normal tothe surface defined by the first and second axes.

43. In the system set forth in claim 39:

the first and secondr'members being planar and being disposed incontiguous relationship to each other.

44. In a system for providing a controlled relative movement between twomembers along first and second coordinate axes, the combination of:

second magnetic means mounted on the second member forinteractingmagnetically with the first member to produce an independentmovement of tlte-second member relative to the first member along thesecond axis simultaneously with the movement of the second memberrelative to the first member, and

third means disposed on the second member and cooperative with the firstmember for maintaining the second member in displaced but contiguousrelationship to the first member.

45. In the s vsten.' set forth in claim 44:

the tltirri means constituting a hydrostatic air bearing.

46. ln the system set forth in claim 44:

the first magnetic means being constructed Io interact with the firstmember in inhibiting the rotation of the second member relative to thefirst member about an axis substantially normal to the surface definedby the first and second axes.

47. In the system set forth in claim 46:

the first and second members being planar.

48. In the system set forth in claim 21:

the first magnetic means being constructed to prevent rotation of thesecond member relative to the first member about an axis substantiallynormal to a surface defined by the first and second axes,

49. In a system for providing a controlled relative movement between twomembers along a particular ax'is,

the combination of:

a first member,

a second member spaced from the first member and movable relative to thefirst member along the particular axis and including first magneticmeans disposed on the second member for interacting magnetically withthe first member to drive the second member relative to the first memberalong the particular axis and second magnetic means disposed on thesecond member and cooperative with the first magnetic means forinteracting magnetically with thev first member to inhibit rotation ofthe second member relative to the first member on any axis substantiallynormal to the surface of the first member, and

second means far providing for a selective energizing a] the first andsecond magnetic means to. obtain a driving of the second member relativeto the first member along the particular axis.

50. In the system set forth ln claim 49, the ,rst and second membersbeing planar and being disposed in contiguous relationship to each otherand the particular axis being linear.

51. In the system set forth in claim 49, the first magnetic 'means beingcooperative with the first member for providing for the determination ofthe position of the second member relative to the first member along theparticular axiswhile driving the first member relative to the secondmember along the particular axis.

52. In a system for providing a controlled relative movement between twomembers along a particular axis, the combination of:

' a first member,

a second member spaced from the first member and movable relative to thefirst umember along the particular axis and including first magneticmeans disposed on the second member for interacting magnetically withthe #rst member to drive the second member relative to the first memberalong the particular axis and to simultaneously provide for adetermination of tlte position of the second member relative to thefirst member along the particular axS,

second means for providing for a selective energizing of the firstmagnetic means to obtain a driving of the second relative to the firstmember along the particular axis, and

third means disposed on the second member for provding an air bearingrto maintain the second member in displaced butcontiguous relationship tothe f first member.

53. In thesystem set forth in claim 52 the first magnetic meansincluding atleast one winding for selectively energzing the firstmagnetic means.

54. In a system for providing a controlled relative indication ofdisplacements between two members along first and second coordinateaxes, the combination of:

a first member,

Va second member disposed relative to the first member for independentdisplacement between the first and second members along each of thefirst and second coordinate axes,

first magnetic means operatively coupled to a particular one of thefirst and second members and ctnfiprrative niilz the other one of thefirst and second tnt/:titers for producing a magnetic interactionbelli-cen thc first magnetic means and the other meml-rr to provide foran independent indication of a displacement between tlze first andsecond members along the first coordinate axis, and

second magnetic means operatively coupled to the particular one of thetrst and second tnctatbers and cooperative with the other one of thefirst and second members for producing a magnetic interaction betweenthe second tnagneticmeans and the other memt'vcr to provide for anindependent indication of o displacement between .the first and secondmembers along the second coordinan-.axis simultaneously with thedisplacement between first and second members along the first coortiin.c axis.

55. it.' the system set forth in claim 54:

the other one of the rst and second members having magnetic propertiesand the rst and second magnetic means being provided with magneticproperties and being respectively provided with first and secondwindings for cooperating with the other one of the ,first and secondmembers to provide for an indication of displacement between the firstand second members respectively along the first and second axis.

56. in the system set fort/1 in claim 55:

t/tr hrs! magnetic means having properties of becoming .wlrctivteiytint/mimi ity tlm first winding and of prt tiucintt magnet/t: lines offarce, when energized, for loper/ning with the other one o/ the firstont! second members to provide for an indication of a tiisplacementbetween the rst and second members'along the first coordinate axis andthe second magnetic means having properties of becoming seleciivel yenergized by the second winding and of producing magnetic lines offorce, when energized, for cooperating with the other one of the firstand second members to provide for an indication of a displacementbetween tite first and second members along the second coordinate axis.

57. ln a system for providing a controlled relative indication ofdisplacement between two members along first and second coordinate axes,the combination a first member,

a second member disposed in contiguous relationship to the first memberfor independent displacement between the first and second members alongeach of the first and second coordinate axes,

a plnrality of first magnetic means provided in the first member atspaced positions along the first and second coordinate axes to define amagnetic grid,

second magnetic means provided in tite second mem'- ber at spacedpositions along the first coordinate axis, said second magnetic meansbeing selectively ertergized and being disposed at particular positionsrelative to contiguous ones of the first magnetic means and cooperativewith the first magnetic means, when selectively energized, forinteracting magnetically with the first means to provide for indicationsof displacements betweeii'the first magnetic means and the secondmagnetic means along the first coordinate axis, and

third magnetic means provided in the second memberv at spaced positionsalong the second coordinate axis, said third magnetic means beingselectively energized fCo l and being disposed at particular positionsrelative tc 58. In the system set forth in claim 5 7:

e first member defining a magnetic grid structure and each of the secondmagnetic means respectively having at least a pair of elements forinteracting with the magnetic grid structure of the first member toprovide for an indication of displacement of the first member relativeto the seco/:ci member along the rst axis, the elements in the secondmagnetic means being displaced relative to each other and to titemagnetic grid structure of the rst member to provide for tite indicationof displacement of the second member relative to the first member alongthe first axis, each of the third magnetic means respectively having atleast a pair of elements for interacting with the magnetic gridstructure of the first member to provide for an indication ofdisplacement of the first member rela tive to the second member alongthe second axis, the elements ln the third magnetic means beingtit'sp/tnfrti rf'ltitlvc to cach other and lo the magnet/i tti'it/.vlrntw tnrr of the first member tn pnwiiic for thv int/imitan oftllsplttmnnenty ci the recanti mein/wt' relativ@ tn the first memberalong tint second tts-it.

59.1n the system srt for/lt in cial/n 2o:

tite first member having magnetic cimracteri'ttics and the secondmagnetic means including windings and having magnetic characteristicsfor interacting with the first member to provide for indications of'displacementsbetween the first and second members along the first axiswhen selectively energized and the third magnetic means includingwindings and having magnetic characteristics for interacting with thefirst member to provide for indications of displacement..- between thefirst and second members along the secdnd ,axis when selectivelyenergized and the first member being planar.

References Cited The following references, cited by the Examiner, are ofrecord in the patented fle of this patent or the original OTHERREFERENCES Thompson, L. I.: Technical Disclosure 1964. pp. 19-20.

Linear Incremental Motor, IBM Bulletin. vol. 6, No. 9, February,

JOSEPH W. HARTARY, Primary Examiner U.S, Cl. X.R.

fll le.

